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Moog Animatics’ Knowledge Base

This is your online source for all information needed to become a motion control expert.

From understanding SmartMotor™ torque curves and motor sizing to cable configurations and OEM Dynamics linear actuator training videos, Moog Animatics’ Knowledge Base exists to support our customers in any and every question or concern they may have and provide every explanation before you even pick up the phone.

If there is any other information you believe would be helpful to have in the Knowledge Base,
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, and we will do our best to supply the needed information.

In addition to our Knowledge Base, we have an extensive library of case studies available here:

Cables

Each SmartMotor has a primary RS232 serial port and a secondary RS485 port by re-assignment of ports E and F of the 7 I/O points. Up to 100 SmartMotor servos may be separately addressed and are identifiable on either RS232 or RS485.

The most common and cost effective solution is typically RS232 serial communications. Under this structure, each motor is placed in an electrical serial connection such that the transmit line of one motor is connected to the receive line of the next. Each motor will be set to "echo" the incoming data to the next motor down with approximately 1 millisecond propagation delay. There is no signal integrity loss from one motor to the next, which results in highly reliable communications.

How to Choose Power Supplies

Which is better, Linear or Switcher Supplies?

Since servo motors are inductive they may run highly dynamic motion profiles. As a result, their current demand can vary widely. Surge currents from stand-still to maximum load may be extremely high, yet steady state curret demand over time may be relatively mild. As a result, proper care should be taken when selecting power supplies.

Moog Animatics offers two basic types of power supplies.

The below chart gives a brief comparison of the two types of supplies.

Linear

Switcher

AC Input

Field selectable(120/240VAC)

Universal90-240VAC

Power Factor Corrected

NO

Yes

Relative Size

Big and bulky

Lightweight

Cooling

Ambient Convection

Fan cooled

Surge Capacity

400%

5%

Voltage Regulation

15% Drop over range

0%, fixed8

Shunt Required?1

Occasionally,but not typically

In most cases,highly recommended

1See Shunt Section for more information!

Voltage Drop Comparison

As seen in the graph to the right, Linear (Unregulated) suppllies can handle large surge current loads. This is because linear supplies typlically contain large output capcitors to handle those surges well.

Voltage regulations: Switchers are highly regulated supplies. They will maintain fixed voltage until they reach maximum load and then will "crowbar" to zero volts to protect the output stages. Linear supplies will slowly drop in output voltage while supplying more and more current.

This is the most funamental difference between switchers and unregulated supplies.

Even though a switcher cannot handle the higher current surges, if it can ouput as much current as you would expect for a given servo application, then they will actually help the servo accelerate much faster because system voltage will be maintained at maximum level.

However, if your servo application requires surge currents in excess of 50 Amps or more, the switchers may not be cost effective. Getting 50 amps from a Moog Animatics 20 Amp supply is easy. Getting 50 Amps from Moog Animatics switchers would require placing multiple units in parallel, so it may not be cost effective to do so.

Intro to Shunts

Moog Animatics offers several shunt options for use with DC input servo motors.

Shunts are needed to protect the servo controller and drive stages from over voltage.

Over voltage sources originate from the following:

Back EMF due to back driving the motors

Sudden or hard decelerations

Hard stop crashes (immediate deceleration to zero speed)

Vertical load drops

The shunts actually add an additional load to the DC bus automatically when voltage exceeds the trigger level by connecting large load resistors across the bus. Trigger voltage is typically 49.5VDC. As a result, the shunts will work with any of the supplies we offer.

The switcher supplies have an adjustable output trim pot. If used with our shunts, the output voltage MUST BE adjusted to <=48vdc to="" insure="" the="" shunts="" do="" not="" stay="" gated="" on="" span="">

Shunts cannot be placed in parallel with each other to increase capacity. The shunt with the slightly lower trigger voltage will trigger first while the other shunt never triggers at all. Please consult factory for information on how to deal with larger shunt requirements.

Shunts should always be placed between the motor input and any disconnect or e-stop relay to insure protection of the motor when power is not applied or e-stop relay contacts are open.

Back EMF

The Real story about Back EMF:

Generally speaking, back EMF is the voltage generated in a motor when it spins. This voltage is typically propotional to speed. However, this is a general rule. The truth is that the back EMF voltage is proportional to the rate of change of magnetic flux in the windings of the stator. As a result, consttant speeds produce contant and predictable voltages. However, sudden changes due to decelerations or hard stop crashes cause an immediate change in magnetic flux or even a total instantaneous collapse. As a result, voltages can go 5 to 10 times higher than spinning the motor at its maximum speed.

For this reason alone, it is highly recommended to use a shunt in all vertical load applications or any case where the motors could be stopped quickly or back driven suddently.

We offer both open frame and enclosed shunts in 100Watt and 200Watt capacities. The shuns are all automatic and get their power from the DC bus they are attached to. They simply need to be placed in parallel with the DC bus.